Page:Popular Science Monthly Volume 28.djvu/565

Rh any piers ever built, and through a medium of the most treacherous character. New plans had to be devised to secure success. One pier, weighing forty-five thousand tons, was sunk to a depth of one hundred and thirty-six feet below high-water mark through ninety feet of sand and gravel; and another one, weighing forty thousand tons, to one hundred and thirty feet through eighty feet of deposit. The loss of life which occurred in the caisson of the east pier resulted from the fact that the situation at such a depth, with the air-pressure it was necessary to endure, was entirely new, and there was no recorded experience by which operations could be guided safely. The erection of the arches developed new problems. The arches had to be designed about two and a half inches longer than they are in their present position, because of the contraction which their weight causes throughout the arch. Each half of the arch was built out from the pier and suspended by guys passing through heavy masts erected on each pier, and the central tubes had to be specially fitted for insertion. The suggestion was made by his chief assistant to contract the tubes by boxing them up and covering them with iron. This Mr. Eads disapproved of, and devised telescopic tubes for the center of the arch which could be shortened by an internal right and left hand screw-plug, and afterward extended by powerful levers to rotate this plug, steel bands being also provided to cover the plug, flush with the outside of the tube, when the tubes were properly distended. During his absence in London, the chief assistant, confident of his ability to close them with ice, and, having been left with full authority, undertook to do so; but the attempt proved a failure after a trial of eight or ten days, and the telescopic tubes, which Mr. Eads had prepared, were then inserted without difficulty.

In an address delivered at the opening of this bridge, July 4, 1874, Mr. Eads revealed that confidence in his resources and investigations which probably furnishes one of the keys to the secret of his success in this and in his other enterprises. This secret consists in the fact that his courage is always equal to his convictions. Everything, he said, on this occasion, which prudence, judgment, and the present state of science could suggest to him and his assistants had been carefully observed in its design and construction; every computation involving its safety had been made by different individuals, thoroughly competent to make them; they had been carefully revised, time and again, re-examined, verified, until the possibility of error nowhere existed.

A similar confidence was displayed in his plans for deepening the mouth of the Mississippi by jetties, in which he was opposed by nearly all of the United States engineers, and by a commission of seven of them. The commission in 1874 proposed to avoid the bars by building a canal from Fort St. Philip to Breton Bay. Mr. Eads's plan was to make the river itself deepen a channel through them. Congress